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United States Patent 3,097,549 COLD MILL PRESSURE CONTROL Edwin B. Hudson, Middletown, Ohio, assignor to Armco Steel Corporation, Middletown, Ohio, a corporation of Ohio Filed Apr. 23, 19518, Ser. No. 731,319 4 Claims. (Cl; 80--60) This invention relates to the operation of a cold reduction mill to produce strip having a uniform gage across the strip. In particular, the invention relates to a reversing mill wherein a given strip or coil of steel is passed back and forth a predetermined number of times until the desired final gage is obtained. It will be apparent, however, as the description proceeds that the principles involved will be applicable to other types of mills, such as tandem mills, although in the description which follows I shall describe the invention as it applies to a reversing mill.

In the operation of a cold reduction reversing mill it is the general practice to make reductions in the coil or strip in terms of percent reduction. This practice is relatively successful where heavier gages are encountered, for example, .020" and thicker. However, to roll accurate cross gage requires great skill on the part of the operator, for when he adjusts the mill screws to get the desired percentage reduction the screw pressure changes to values which deflect the back roll to a greater or lesser degree than is required to suit the crown or longitudinal curvature of the work rolls. While such variations may be corrected by heating the back roll when the back roll deflection is too great, or cooling the back roll when the deflection is too little, these heating and cooling operations are relatively ineffective in that the available time in which the operations may be carried out is too short. When the deflection of the back roll is of lesser degree than is required to suit the crown of the work rollwhich effectively renders the work roll crown too highthe center of the strip rolls longer than the edges, a condition which is indicated by buckles in the strip surface. On the other hand, when the deflection of the back roll is of a greater degree than is required to accommodate it to the crown of the Work roll, the crown becomes effectively too, low, and the edges of the strip roll longer than the center and this is evidenced by ruffled edges in the strip. The net result is a never ending effort on the part of the operator to correct for crown in the work roll, and it is seldom that a rolling pass is made when the screw pressure and the back roll deflection actually suits the Work roll crown.

It has been my observation that the fallacy of the method characterized above lies in the fact that the work roll crown is always constant, whereas the screw pressure is infinitely variable. Consequently, for every degree of Work roll crown there is a screw pressure which accommodates the back roll exactly to the crown. In a reversing mill, for example, between every roll change the work roll crown is fixed or constant excepting, of course, for wear, and the cross sectional dimensions of the roll cannot be changed except by changing the roll itself. The operator can, however, change the screw pressure at will and thereby alter the degree of deflection of the back roll. From this it follows that if the operator can be provided with a way of accurately ascertaining the precise amount of screw pressure to apply for any give work roll crown, he may readily adjust the screw pressure to suit the work roll crown that is being used at the moment and effect precise conformity between such work roll crown and the back roll.

It is, therefore, a principal object of the instant invention to provide a procedure by means of which the 3,097,549 Patented July 16, 1963 mill operator may determine the proper screw pressure load to accommodate the backing rolls of the mill to a set of working rolls having a given crown.

A further object of the invention is to provide means to determine the back roll deflection for all degrees of screw pressure so that the operator will have available information which will enable him to accurately suit the back rolls of the mill to the crown of the work rolls for any given width of strip being handled by the mill.

Still a further object of the invention is the provision of a procedure by means of which the deflection of the backing rolls can be measured for all degrees of screw pressure for each width of strip to be handled by the mill and this information plotted as a family of curves which may be used by the operator to. apply the proper screw pressure for any given work roll crown.

The foregoing together with other objects of the in vention which will appear hereinafter or which will be apparent to the skilled worker in. the art upon reading these specifications, I accomplish by that construction and arrangement of parts and by those procedures of which I shall now describe exemplary embodiments,

Reference is now made to the accompanying drawings wherein:

FIGURE 1 is an elevational View illustrating a mill. in accordance with the invention.

FIGURE 2 is a side elevational view of the mill shown in FIGURE 1 taken from the operators side.

FIGURE 3 is an. enlarged fragmentary elevational view illustrating a screw pressure gage operatively connected to the mill screws.

FIGURE 4 is an elevational view illustrating in exaggerated form the deflection of the back rolls and the means for measuring the back roll deflection under load.

FIGURE 5 is a load and deflection. chart illustrating the manner in which the information obtained is plotted so that the operator may accurately ascertain the screw pressure to be applied for strip of various widths.

Briefly, in the practice of the invention, for. testing.

purposes the mill is provided with a set of work rolls which are. ground as cylinders and have no crown. With these test rolls in the mill, test sample sheets of the desired widths are inserted between the test rolls and readings are taken of the back roll deflection over a wide range of screw pressures. This deflection information is then plotted as a family of curves which will be used by the operator to apply the proper screw pressure for any given work roll crown. This practice is followed up to the. last pass when the screws are set, regardless of screw pressure, to produce the desired gage. The previous passes before the last percentage pass will insure a uniform gage across the strip.

Referring now to the drawings, the mill stand shown in FIGURES 1 and 2 is a small work .roll type for rolling extremely thin gages. Its design is similar to the mill disclosedin Hudson Patent 2,685,807, issued August 10, 1954, and entitled Four-High Rolling Mill. As already indicated, however, the particular type of mill employed does not constitute a limitation on the invention.

The mill housings are shown at 1, complete with screw down having mill screws 2, top back roll chuck 3, top back roll 4, top work roll 5, bottom work roll 6, bottom back roll 7, and bottom back roll chucks 8. The mill housings 1 are preferably mounted on mill shoes 9. The back rolls 4 and 7 are driven, as seen in FIGURE 1, by spindles 10 and 11 which, it will be understood, are connected to suitable driving means (not shown).

In accordance with the instant invention, a screw pressure reading device 12 is operatively connected through connectors 13 to strain gages 14 interposed between the mill screws 2 and the back rolls 4 and 7. The screw pressure device 12 is provided with a pair of pointers 15, 15a arranged to show screw pressure on each side of the mill. Preferably, the pressure gage will be calibrated in units of 100,000 lbs. As seen in FIGURE 2, the pressure indicating device may be conveniently mounted on the operators side of the mill housing.

Referring now to FIGURE 4, the backing rolls 4 and 7 are illustrated as being deflected by the rolling load L applied to the opposite ends of the backing rolls, the deflection of the rolls being measured by deflection gage 16 provided with a micrometer 17 from which the amount of deflection d may be read.

In accordance with the invention, the deflection of the backing rolls 4 and 7 is measured using a set of test work rolls a, 6a which are ground as cylinders and have no crown. The test strips are placed between these test rolls and readings are then taken of the back roll deflection over a wide range of screw pressures. Preferably the test strips will be sheets having a thickness of about .090", the test strips varying in increments of 6" from the minimum to maximum widths to be handled by the mill.

FIGURE 5 shows a chart plotted from information obtained using test samples ranging from 36" to 72". As seen therein the screw pressure load L is plotted against the back roll deflection d, and as will be apparent from the chart, where a 60 wide strip is to be run a screw pressure or load of 600,000 lbs. is required to produce a deflection of .0175". Of course, once the chart has been established for a given set of backing rolls, the operator may then select the work rolls having the desired crown for the reduction to be accomplished. For example, if we assume that the strip is 60" wide and is to be acted upon by work rolls having a crown of .0020", the operator, by consulting the chart will find that the proper screw pressure to be applied is 6705000 lbs. If, on the other hand, the same set of crown work rolls are to be used to roll strip having a width of 48", the chart indicates that the proper pressure is 850,000 lbs. At this pressure, the backing rolls will be deflected by an amount equal to the crown in the working rolls so that the contact line of the rolls against the strip being rolled is a straight line. It will be understood that in a reversing mill, the screw pressure will be changed with each change in the work roll excepting for the last pass when the screw pressure is set to provide the desired final gage.

In the exemplary embodiment shown in the drawings, it will be understood that once the deflection characteristics have been determined, the cylindrical test rolls 5a, 6a will be replaced by crowned working rolls and the strip 18 will be passed back and forth between the mill coilers '19, the strip passing over the line supporting rolls 20, as will be well understood by the worker in the art. In addition, it will be understood that if the strip is tapered as it is received from the hot mill, it is within the scope of the invention to make one pass in the hitherto normal manner, i.e. percentage reduction, to remove gage variations between the leading and trailing ends of the strip. By this I mean rolling the strip to a constant thickness before initiation of the cold reduction passes to reduce the strip to final gage. Or, if it is desired to retain the shape of the strip as that which is produced by the proper screw pressure, then means should be provided for tension variation between the leading and trailing ends of the strip. The desired gage can then be produced by a combination of screw pressure and tension control in the well-known manner.

Modifications may be made in the invention without departing from the spirit of it. Having, however, described the invention in an exemplary embodiment, what I desire to secure and protect by Letters Patent is:

1. A method of producing strip having a uniform gage across its width, which comprises providing a mill having crowned work rolls, back rolls, and screw means for applying pressure to said back rolls, pre-setting said screw pressure means to deflect said back rolls by an amount equal to the crown of said work rolls, whereby for each pass of the strip therebetween the work rolls will make substantially straight line contact with the strip, rolling the strip between said work rolls and maintaining the same pre-set screw pressure for as many passes as required to bring the strip to substantially final gage, and when said strip is substantially to final gage, making a last pass through said mill which is a percentage reduction to final gage.

2. The method claimed in claim 1 wherein the setting of the screw pressure means to deflect the back roll by an amount equal to the crown of the work rolls is established by initially fitting the mill with a set of test work rolls which are cylindrical and uncrowned, placing between said test work rolls a test piece of strip stock having a width equal to the width of the strip to be rolled, holding said test piece of strip stationary, applying pressure to the back rolls of the mill by means of said screw means, and establishing the pressure necessary to deflect .the back rolls by an amount equal to the crown of the Work rolls to be used to reduce the strip, removing the said test work rolls and replacing them with the crowned work rolls, and pre-setting the screw means to the value established by said test rolls and said test piece of strip stock.

3. The method claimed in claim 1 wherein the strip is subjected to an initial percentage reduction pass to remove gage variations between the leading and trailing ends of the strip.

4. In a method of rolling sheet material to a desired gage which is of substantially uniform thickness throughout its width, said rolling being conducted in a mill having crowned work rolls, back rolls, and screw means for applying pressure to said back rolls, the steps which compmise pre-setting said screw means to develop the pressure required to deflect said back rolls by an amount equal to the crown of said work rolls, and there-after rolling the strip between said work rolls while maintaining the same pre-set screw pressure for as many passes as required to bring the strip to substantially the desired gage.

References Cited in the file of this patent UNITED STATES PATENTS 581,078 Menne Apr. 20, 1897 1,781,809 Detwiler Nov. 18, 1930 2,430,410 Pauls Nov. 4, 1947 2,673,480 Wellman Mar. 30, 1954 2,691,326 McArn Oct. 12, 1954 2,903,926 Reichl Sept. 15, 1959 

1. A METHOD OF PRODUCING STRIP HAVING A UNIFORM GAGE ACROSS ITS WIDTH, WHICH COMPRISES PROVIDING A MILL HAVING CROWNED WORK ROLLS, BACK ROLLS, AND SCREW MEANS FOR APPLYING PRESSURE TO SAID BACK ROLLS, PRE-SETTING SAID SCREW PRESSURE MEANS TO DEFLECT SAID BACK ROLLS BY AN AMOUNT EQUAL TO THE CROWN OF SAID WORK ROLLS, WHEREBY FOR EACH PASS OF THE STRIP THEREBETWEEN THE WORK ROLLS WILL MAKE SUBSTANTIALLY STRAIGHT LINE CONTACT WITH THE STRIP, ROLLING THE STRIP BETWEEN SAID WORK ROLLS AND MAINTAINING THE SAME PRE-SET SCREW PRESSURE FOR AS MANY PASSES AS REQUIRED TO BRING THE STRIP TO SUBSTANTIALLY FINAL GAGE, AND WHEN SAID STRIP IS SUBSTANTIALLY TO FINAL GAGE, MAKING A LAST PASS THROUGH SAID MILL WHICH IS A PRECENTAGE REDUCTION TO FINAL GAGE. 